The invention relates to a method and a device for extracting a liquid out of a tube of great length, closed at one of its ends, in all the cases where a communication between this closed end and a source of a substitution fluid cannot be easily established.
Such a device can for example be applied for evacuating liquids out of tubes taken down in deep wells. It is particularly interesting in the petroleum field where tubings are used for numerous applications, be it for supporting drill bits, outfitting wells for production, or guiding measuring tools taken down for tests during the drilling process or during the production stage.
In order to test a well during the drilling stage, it is well-known to take down to the level of the layers to be tested a sampler comprising a tubing closed at its base by a controlled opening valve and equipped on its circumference with a deformable closing device of the packer type. This device is adapted, in the expansion position, for closely leaning against the wall of the drill hole or the casing when such casing exists and thus for keeping the tubing in position. A pressure-measuring element is placed at the tubing base. The pressure within the tubing, at its base, when the valve is closed, equals the atmospheric pressure if the tube does not contain any water. It can be increased at will by filling part of the tubing with water in order to limit the pressure difference on either side of the valve to a determined value.
On account of the depression at the basis of the tubing in relation to the pressure in the well, a suction occurs at the valve opening and the pressure in the well undergoes a very substantial decrease which is at least partly compensated by the tested formations after a given delay which characterizes the rock permeability. Several successive valve opening and closing cycles are achieved. An analysis of the evolution in terms of time of the measured pressure and flow rate allows to characterize a geologic formation, as it is well-known by the man skilled in the art. Once the test has been carried out, the pressures on either side of the packer must be balanced before taking up the sampler, emptying the tubing and taking the set down again if new tests must be achieved at another depth. When several successive tests are necessary in the same well, the time between the actual measurings is very long because of the numerous necessary operations.
The principle of the evacuation of a tube by extracting its content by means of a mobile plunger displaced in the tube is well-known. It cannot be performed easily without connecting the base of the tube with a source of a substitution fluid such as a gas for example, and introducing it behind the piston as the evacuation is carried out. In all the cases where the base of the tube is little accessible and notably in the application described above, where the tubing is very long and taken down in a narrow well, setting up any piping allowing a connection with a gas source often proves to be difficult, if not unworkable in practice.